Crossbones is a world-class hand-to-hand fighter with extensive experience in street-fighting and various martial arts and military combat techniques. He is an expert pilot and a marksman with crossbows, guns and throwing knives.

Weapons

His weaponry includes various firearms, a collapsible crossbow, a wrist spike, spring-loaded stiletto blades in his gauntlets, various explosives and poisoned knives.

Paraphernalia

Carries various communications devices, one of which is mounted in one of his gauntlets.

Young Brock Rumlow led the Savage Crims gang on New York's lower east side. After he brutalized fifteen year old Rachel Leighton, two of her brothers assaulted Brock; the eldest brother was killed. Rumlow fled, entering the Taskmaster's school for criminals, and within three years became an instructor there under the name Bingo Brock. As a mercenary, he enlisted with the communistRed Skull (Albert Malik) in Algeria, serving him as "Frag" until he was sent to invade Arnim Zola's Switzerland chateau. Ultimately the only team member to survive the assault, Rumlow there met and impressed the NaziRed Skull (Johann Shmidt); this Skull accepted Brock’s services, code-naming him “Crossbones.”

Sent to retrieve the five Bloodstone fragments, Crossbones shadowed Helmut Zemo’s search for them. While Zemo battled Captain America, Crossbones knocked out Captain America's pilot, John Jameson, and stole two fragments; when he got near the other three, the five combined to re-animate Heinrich Zemo's corpse under control of the alien Hellfire Helix. Unobserved, Crossbones destroyed the Helix (worn on the corpse's forehead) with a crossbow bolt. Brock then kidnapped Diamondback (whom he recognized as Rachel Leighton), using her as bait to trap Captain America; but when the Skull learned of Crossbones' involvement with the Captain, he ordered Crossbones to flee. Crossbones recruited the Controller and Voice of Doom to serve the Skull, led the Skeleton Crew against the Hellfire Club’s Selene, and, using psychic Tristam Micawber, located the Skull after Magneto kidnapped him. He attempted assassinating the Kingpin, was stopped by Typhoid Mary, and battled Bullseye when the Kingpin retaliated. He led the Skeleton Crew when they were captured by the Schutz-Heiliggruppe (Blitzkrieg, Hauptmann Deutschland, Zeitgeist); after Arnim Zola rescued them, the Skull faked the assassination of himself, Mother Night, and Crossbones. The Red Skull finally fired Crossbones for questioning the Skull's decision to ally with the Viper.

Crossbones headed east, working briefly in Chicago for druglord Marco Sanzionare against Super Pro. In New York, Crossbones kidnapped and brainwashed Diamondback by abusing her repeatedly and forcing her through a rigid combat training routine. Forcing Diamondback to steal Captain America's super-soldier treated blood from Avengers Mansion, Crossbones returned to the Skull. When the Skeleton Crew's new leader, Cutthroat, plotted Crossbones’ murder, Mother Night warned Brock, who slit Cutthroat's jugular. Diamondback escaped, summoning Captain America and the Falcon to capture the Skull’s operatives; Crossbones was imprisoned, but eventually convinced officials he was rehabilitating, partly by defeating the terrorist cell "Fortress" when they invaded a Denver hospital. Exploiting his jailors’ gullibility, Crossbones escaped, and was hired by Hydra to bomb New York's embassy row alongside the Absorbing Man, but the pair was stopped by Captain America. Betrayed by Hydra, Crossbones fled, wreaking vengeance on his bosses. He was hired by New Son to assassinate Gambit, but despite allying with Batroc and Zaran, was defeated by the combined efforts of New Orleans' assassin's and thieves’ guilds; Crossbones was imprisoned in the Raft until Electro's break-in freed him. The Skull promptly rehired him,he was sent to federal building during a riot along with red skulls daughter also his girlfriend, he fought bucky barnes(the new captian america) who almost ended up killing him by shooting him 4 times in the chest which put him into custody. when freed he was aiding the red skull with the cosmic cube when capptian america assasinated the Red Skull and stole the Cube. Lukin anonymously blamed Captain America for the Skull’s death, but Crossbones soon realized the truth and now appears to be hunting Lukin.